The Ni-Hon-Sea-Tai project is a coordinated series of epidemiologic studies on dementia that include a survey in the Adult Health Study Cohort of the Radiation Effects Research Foundation (RERF) in Hiroshima. The project was organized by the Asia-Pacific Office and is continued as a shared effort by cooperating scientists in Seattle, Kawasaki City, Taipei, Hiroshima, and Honolulu. A central goal is to develop and use methods sufficiently alike so that comparisons of rates and patterns of dementing illnesses across sites would be possible. Coordination with the Hiroshima study was facilitated by establishment of an interagency agreement with the Department of Energy, through which funds were made available to the RERF for work related to our collaborative studies on dementia. A large part of these funds were used to support the participation of Japanese scientists in the Sixth Japan-U.S. Workshop on Methods for Cross-National Dementia Research. The project is progressing well and it is likely that parallel studies using comparable methodologies will be conducted at two sites in the U.S., one or two sites in Japan, and at least two sites in Taiwan.